The present invention relates to a composition comprising at least one emitter compound and at least one polymer having conjugation-interrupting units, to the use of this composition in an opto-electronic device, and to an opto-electronic device which comprises this composition according to the invention.
Both singlet and triplet emitters are known as possible emitter compounds from the prior art. In recent years, organometallic complexes which exhibit phosphorescence instead of fluorescence are increasingly being employed as emitting materials in opto-electronic devices (M. A. Baldo et al., Appl. Phys. Lett. 1999, 75, 4-6). Triplet emitters which are known from the prior art are usually metal complexes, since, in particular, heavy metals favour triplet transition. In general, however, there are still considerable problems in the case of OLEDs which exhibit triplet emission. Thus, the physical properties of phosphorescent emitters are still inadequate for use in high-quality and long-lived electroluminescent devices with respect to the stability of metal complexes, efficiency, operating voltage and lifetime. Further improvements are therefore necessary here. Further improvements are also still necessary in the case of other compounds used in organic electroluminescent devices, such as, for example, matrix materials and charge-transport materials. In particular, the matrix materials must be matched to the emitter compounds used, since otherwise undesired quenching effects may arise.
Conjugated polymers have already been investigated intensively for some time as highly promising materials in OLEDs. Their simple preparation promises inexpensive production of corresponding electroluminescent devices. However, conjugated polymers used and known to date have the disadvantage that the achievable efficiency has a certain upper limit. This is, in particular, at the HOMO-LUMO separations and at the singlet and triplet energy levels of the polymer and the emitter compound. For example, if the triplet level of the polymer is lower than that of the emitter, the triplet energy of the emitter can be transferred to the polymer by an energy-transfer mechanism. The phosphorescence is thus quenched.
The best-known polymer triplet matrix is PVK (polyvinylcarbazole) (Yang, X.; Neher, D.; Hertel, D.; Daeubler, T. K.; Highly efficient single-layer polymer electrophosphorescent devices; Adv. Mater. (Weinheim, Ger.) 16[2], 161-166. 2004). This is a non-conjugated polymer.
U.S. Pat. No. 7,250,226 B2 discloses a triplet emitter polymer which has hole-transport, electron-transport and emitter units in the side chain of the polymer.
Wai-Yeung Wong et al., Macromolecules 2004, 37, 4496-4504, propose employing polymers having fluorene units as conjugation interrupters, where the triplet emitter unit is incorporated into the polymer chain.
JP 2001/257076 discloses an OLED comprising a non-conjugated polymer as host and a metal complex with group VIII metals as dopant. Polyvinylcarbazole is disclosed as non-conjugated polymer matrix.
None of these systems exhibits optimum electro-optical properties (for example adequate efficiency) and all have deficits with respect to their stability. In particular, the polymers which have functional units in the main or side chain of the polymer are, in addition, difficult to prepare.